Among those groups being the super dedicated wotaku who will buy multiple copies of stuff in order to see their oshimen do well. The same can be said of any of the other idols, but AKB48 is crafted specifically for these... 'eccentric' people. Sales isn't a very good way to measure "success" in the sense of influence or popularity. There is a lot of super-fan "interference" in those numbers.

Whatever the case, Sae had great sales and in the end that's more important than why.